Control apparatus and method for unloading compressors



May 8, 1962 J. RAUFEISEN 3,033,217

CONTROL APPARATUS AND METHOD FOR UNLOADING COMPRESSORS Filed Feb. 16,1959 2 Sheets-Sheet 1 4 g, 1 T0 CONDENSER [720M .Z'VAPDFA-TOR 2W0 LdBRC/ITION 5Y5 TEM lhzxaniar Jase OZ Eauf'esem. 2 I

May 8, 1962 .1. RAUFEISEN 3,033,217

CONTROL APPARATUS AND METHOD FOR UNLOADING COMPRESSORS Filed Feb. 16,1959 2 Sheets-Sheet 2 J0s'90 Raufez'sew United States Patent 1 3,033,217CONTROL APPARATUS AND METHOD FOR UNLGADING CGMPRESSORS Joseph Raufeisen,Palatine, Ill, assignor to Bell & Gossett Company, a corporation ofIllinois Filed Feb. 16, 1959, Ser. No. 793,570 4 Claims. (Cl. 137-82)This invention is concerned with a variable capacity control forcompressors and, more particularly, relates to a capacity control formultiple-cylinder compressors in which the control varies the loading ofall of the cylinders simultaneously to maintain balanced relationshipsbetween cylinders.

In the preferred form, the capacity control system is automaticallyresponsive to predetermined changes in the system load forvarying thecompressor loading in corresponding predetermined increments.

In prior art unloading systems, a multiple-cylinder compressor ispartially unloaded by completely disabling one of the cylinders, andthis limits the selectivity and adjustment range of the load-regulationsystem while introducing dynamic unbalance into the compressorarrangement.

The principal object of the present invention is to provide an unloadingsystem for a compressor wherein each cylinder is partially unloaded,with the unloading adjustment for each of the cylinders beingaccomplished simultaneously to maintain balanced loading relationshipsbetween cylinders.

Another object is to provide a compressor arrangement wherein a singlecontrol mechanism operates the unloader equipment for a plurality ofcylinders simultaneously.

Still another object of the invention is to provide an arrangementwherein the unloader equipment is actuated through the medium of oilsupplied under pressure from the compressors lubrication system, oilpressure being required to maintain the cylinders fully loaded, andsince thereis no oil pressure when the compressor is at rest, thecompressor starts at its unloaded condition.

Briefly, the unloading system in accordance with this inventionaccomplishes its loading or unloading functions, respectively, bycovering or uncovering a fluid passage in the cylinder sleeve. When thisfluid passage is uncovered, direct communication for the compressiblefluid is established from the cylinder to the crankcase to disable thecylinder during the initial phase of the compression stroke and providecorrespondingly reduced capacity.

In the simplified embodiment illustrated herein for purpose ofdisclosure, a one-step fifty percent capacity reduction is provided,though it is contemplated that a multiplestep unloading arrangement maybe provided where desired by forming the cylinder with a number of fluidpassages at lengthwise spaced points therealong. A multiple-positioncontrol valve mechanism would actuate the multiple-step unloadingarrangement.

Other objects and advantages will become apparent during the course ofthe following description.

In the accompanying drawings forming a part of this specification and inwhich like numerals are employed to designate like parts throughout thesame:

FIG. 1 is a fragmentary, semi-diagrammatic, side-elevational view, withparts broken away and sectioned, illustrating a multiple-cylindercompressor arrangement provided with unloading equipment in accordancewith the present invention;

FIG. 2 is a diagrammatic cross-sectional view of one of the compressorcylinders illustrating the unloader equipment thereon and the controlvalve mechanism for the unloader equipment, with the cylinder beingshown in condition for full-load operation; and

FIG. 3 is a view corresponding to that of FIG. 2 and illustrating thecylinder in condition for partially loaded operation.

Referring now to the drawings and more particularly to FIG. 1 thereof,the invention is illustrated in its application to a multiple-cylinderrefrigeration compressor, though it will be apparent that the inventionis also applicable to compressors having any number of cylinders and torelated types of compressors.

In the arrangement shown, the numeral 10 designates a hollow compressorbody having a crankshaft 11 rotatably mounted therein by any suitablebearing arrangement (not shown), with the crankshaft being adapted forconnection to the output drive shaft of a motor (not shown). In theillustration, the compressor body 10 is broken away to disclose a pairof fluid compression assemblies 12, each of whichincludes a cylinder 13and cylinder head 14, with a piston 15 being reciprocably movablethrough the cylinder to draw in, compress, and discharge a fluid charge.Each piston is connected to the crankshaft 11 by a suitable connectingrod 16.

As is indicated by the labeling of the external connection linearrangement, the compressor unit is adapted for use in an air-coolingsystem. The return line from the evaporator of such a system is shown at17 entering into the crankcase chamber; and the discharge line to thecondenser of such a system, as shown at 18, is brought through a coverplate 19 for the cylinder heads. Each cylinder head contains the usualintake and discharge valves, designated generally as 20 and 21,respectively,

with the intake valve controlling a supply passage 22 between thecrankcase chamber and the upper end of each cylinder.

An unloader apparatus in accordance with this invention, as showngenerally at 23, is applied to each of the cylinders, the unloaderapparatus being controlled by oil pressure delivered from thecompressors lubrication system over the line 24, pressure to this linebeing supplied through a control valve mechanism 25 that is responsiveto changes in the crankcase pressure and correspondingly controls thecondition of loading of the fluid compression assemblies 12. V

As is apparent, the compressor is provided with one control mechanism 25for simultaneously actuating both unloader devices. All of thisequipment is located totally within the crankcase body of thecompressor, with the exception of a control mechanism adjustment whichis brought through the compressor body for convenience of access. Allcontrol piping is internal, and no wiring is required.

The function of each unloader mechanism is to reduce the capacity of itscylinder upon demand from the control mechanism. In the preferredconstructional embodiment of the invention, the unloader mechanism isintegrated into the cylinder sleeve construction and, as is shown inFIGS. 2 and 3, the cylinder sleeve 13 carries an unloader body 27 rigidtherewith and having a lengthwise projecting cylindrical wall section27W cooperating with the cylinder in defining an annular groove thatslidably receives an annular piston-like seal ring assembly 28 and anunloader piston 29 of tubular cylindrical form.

Each cylinder sleeve is provided with coplanar slots 138 that definepassages opening between its compression chamber and the crankcasechamber, and the unloader piston 29 is slidable along the cylinderbetween an unblocldng position (FIG. 3) wherein the slots 133 are openand the fluid compression assembly is operating in a partially unloadedcondition and a blocking position (FIG. 2) wherein the slots are maskedand the fluid gompression assembly is operating in a fully loadedconition.

While these slots are open or uncovered, they aflord direct passage fromthe compression chamber of the 3 cylinder to the crankcase chamber ofthe compressor. During the initial travel of the piston on itscompression stroke, the compressible fluid in the compression chamberescapes into the crankcase. After the piston passes the slots 138, thefluid remaining in the compression chamber is compressed and dischargedinto the line 18.

As indicated in FIG. 3, the unloader piston 29 is normally biased to itsunblocking position by a spring assembly 30 that reacts between anintegral shoulder 13H provided at the head end of the cylinder and anintegral flange 29F provided on the base end of the unloader piston.

The unloader piston 29 is actuated to its blocking position whenever thepressure in the line 24 supplying oil to the base of the unloader body27 is sufiicient to overcome the biasing action of the spring assemblies36. To distribute the actuating pressure uniformly, the wall borderingthe bottom end of the chamber for the unloader piston is formed with anannular groove 276. It will be noted that since the oil pressure in thisline is supplied from the compressors lubrication system, there is nooil pressure when the compressor is starting and the unloader piston 29is in the position in which it is shown in FIG. 3. Thus the compressorstarts partially unloaded until oil pressure is built up and supplied tothe unloading mechanism in accordance with the demands of the controlmechanism.

In a. preferred constructional embodiment, the control mechanism sensescrankcase pressures and controls the flow of oil to the unloadingmechanisms for determining the proper loading of the cylinders. Thecontrol mechanism consists of a pressure-sensing assembly 32 operativelyconnected to actuate an oil control valve assembly 33. Both of theseassemblies are mounted in separate chambers provided in a hollow casing34 that includes an integral attachment flange 34F for anchoring thecontrol mechanism to the crankcase body 19. A divider plate 34?separates the mounting chambers for these assemblies and is apertured asindicated at 34A to accommodate drainage from line 24. Thepressuresensing assembly 32 comprises a bellows 35, an abutment plate 36fixed to the movable end of the bellows, and a pressure spring 37normally urging the bellows towards its extended position. The spring 37is mounted in a cup-shaped seat 38 that is carried on an externallyaccessible adjustment screw 39 which is threadedly engaged in a suitablecover plate 40. A protective cap 39C is removably mounted over the outerend of the screw.

The bellows 35 defines an internal chamber that is open to theatmosphere through vent openings 41 provided in the cover plate 46. Themounting chamber for the bellows is exposed to pressure conditions inthe crankcase of the compressor through vent openings 42 formed in theside walls of the casing 34. Thus, the bellows changes length tomaintain a balance between the crankcase pressure and the combinedeffects of atmospheric pressure and spring pressure. The openings 42also provide a passage for oil draining from line 24 through theapertures 34A.

Adjustment of the crankcase pressure to which the bellows responds iseilected by adjusting the screw 39. After the desired response pressurehas been pre-set, any variation in crankcase pressure such as resultsupon a variation in the refrigeration load causes the bellows to expandor contract correspondingly and shift the abutment plate 36. Forexample, a reduction in crankcase pressure allows the bellows to expand.

The abutment plate engages and .actuates a set of positioning rods 43that project through suitable guide bores extending lengthwise throughthe body of the casing. As will become apparent, these positioning rods43 actuate the control valve assembly 33.

The oil control valve assembly 33 controls the supply of oil from thepressure lubrication system to both unloading mechanisms and thusprovides balanced modulation between full load and reduced loadoperation. The body of the casing 34 forms a hydraulic cylinder for thecontrol valve assembly 33 which includes a floating piston 45 for thiscylinder. The piston is formed with interconnected annular grooves 46that receive oil under pressure from the oil supply line 47. Thebydraulic cylinder is bounded by a head plate 48 that is provided with avent valve passage 49. A pin valve 50 is mounted on an apertured carrierplate 51 that floats in a chambered end cap 52 for the casing under thecontrol of a pressure spring 53. The cap is vented to the crankcase at54.

The head end of the floating piston 45 has a bevelled edge to form apermanent oil chamber, and the oil supply line 47 communicates with thischamber through the grooves 46 and an orifice 56 provided in thefloating piston. Finally, a spring 57 is located in the hydrauliccylinder and normally biases the floating piston against the head plate48 (See FIG. 3) to block flow of oil from the line 47 to the line 24.

The operation of the control mechanism will now be evident. As shown inFIG. 3, when the crankcase pressure rises sufficiently that reducedcapacity operation is called for, the bellows 35 contracts and thespring 53 holds the valve pin 56 in position to block the vent passageof the head plate 48. The head chamber now fills with oil through theannular grooves 46 and orifice 56 in the floating piston 45 and the oilpressure builds up in the cylinder and forces the floating pistontowards the divider plate 34? against the force of the spring 57. Oilnow flows from the supply line 47 through the annular grooves 46 and outthe line 24 to the unloader mechanisms. The unloader piston 29 movesalong the cylinder to block the fluid passages defined by the slots 138.The fluid compression assemblies then operate at full capacity.

When the crankcase pressure is sufficiently low that full-load operationis called for, the bellows will expand and, through the abutment plate36, will drive the positioning rods 43 against the carrier plate 51against the action of the spring 53 to vent the head chamber and allowthe spring 57 to return the floating piston 45 to its original blockingposition (See FIG. 3) wherein it interrupts flow of oil from line 47 toline 24. Oil then drains from the unloader mechanisms, back through theline 24 and out apertures 34A and holes 42 to permit the springs 30 toreturn the unloader pistons 29.

From the foregoing description, it will be apparent that the loadingcondition is determined by the location of the cylinder slots 138 alongthe length of the compression chamber of the cylinder 13. Furthermore,the cylinders 13 are operated in balanced relationship. Anotheradvantage of the invention is that the compressor starts at reducedloading.

The specific embodiment illustrated herein for purposes of disclosure isthe preferred arrangement at present, though it is contemplated thatmany variations in detail may be made without departing from the scopeof the inventive concept. It will be apparent that a multiple-stepunloading arrangement may readily be achieved by providing additionalslots at points spaced lengthwise along the cylinder, and suitablecontrol mechanisms for multiple-step arrangements of this character willbe .apparent to those skilled in the art. The openings in the cylinderfor effecting the unloading may obviously be round holes or of othershape.

It should be understood that the description of the preferred form ofthe invention is for the purpose of complying with Section 112, Title35, of the U.S. Code and that the claims should be construed as broadlyas prior art will permit.

I claim:

1. A control mechanism for supplying lubricant from a source oflubricant under pressure to a point of use in response to changes in areference pressure and comprising a hollow casing forming apressure-sensing chamber and a valve chamber having an inlet forconnection to the source of lubricant and an outlet for connection tothe point of use, said valve chamber having a vent passage, a vent valvein said vent passage, and means normally urging said vent valve intoblocking position in said vent passage, a valve body having one endthereof exposed to lubricant in said valve chamber for shifting movementbetween an unblocking position wherein said inlet and outlet are incommunication and a blocking position wherein said inlet and outlet areisolated, means biasing said valve body to its blocking position, saidvalve body forming a passage for maintaining said inlet and said ventpassage in communication such that when said vent passage is openlubricant normally flows through said inlet and out said vent passageand when said vent valve closes said vent passage, lubricant forces saidvalve body to its unblocking position, and a pressure-sensing mechanismin said pressure-sensing chamber and connected to position said ventvalve in response to changes in said reference pressure.

2. A control mechanism for regulating the supply of fludi from a sourceof fluid under pressure to a point of use in response to changes in areference pressure and comprising casing structure providing separatepressure sensing and valve chambers, said valve chamber having a ventpassage at one end thereof and having an inlet for connection to saidsource and an outlet for connection to said point of use, a vent cap onsaid one end of said valve chamber and spanning said vent passage, acarrier plate movable in said cap and carrying a vent valve for saidvent passage, and means for resiliently biasing said carrier plate to ablocking position in which said vent valve is seated in said ventpassage,'a valve body in said valve chamber for shifting movementbetween a blocking position wherein said inlet and outlet are incommunication and an unblocking position wherein said outlet isisolated, said valve .body having one end only thereof exposed to fluidentering said inlet to develop pressure thereon tending to move saidvalve body towards its unblocking position, resilient means for biasingsaid valve body to its blocking position, said valve body. having apassageway for maintaining said inlet and said vent passage incommunication such that when said vent valve unblocks said vent passagefluid normally flows through said inlet and out said vent passage andwhen said vent valve blocks said vent passage fluid builds up pressureagainst said exposed end of said valve body sulficient to overcome saidresilient means and force said valve body to its unblocking position, apressure sensing mechanism in said pressure sensing chamber andincluding movable in response to changes in said reference pressure andengageable with said carrier plate to position said vent valve inresponse to changes in said reference pressure.

3. A control mechanism for regulating the supply of fluid from a sourceof fluid under pressure to a point of use in response to changes in areference pressure and comprising a casing body providing a pressuresensing chamber at one end and a valve chamber at its opposite end, saidvalve chamber constituting a hydraulic cylinder having a vent passage atone end of said casing body and having a side entrance inlet forconnection to said source and a side entrance outlet for connection tosaid point of use, a piston like valve body having one end in sealinglyslidable relation in said cylinder and having its opposite end exposedto fluid entering said inlet, said valve body being mounted in saidcylinder for shifting movement between an unblocking position whereinsaid inlet and outlet are in communication and a blocking positionwherein said inlet and outlet are isolated, said valve body providing apassageway for maintaining said inlet in communication with said ventpassage, a vent valve in said vent passage, means normally urging saidvent valve into blocking position in said vent passage and mechanism insaid pressure sensing chamber movable in response to changes in saidreference pressure and connected to said vent valve to control theposition thereof such that when said vent valve unblocks said ventpassage fluid flows through said inlet and out said vent passage butwhen said vent valve blocks said vent passage fluid pressure acts on theexposed end of said piston-like valve body to force the same to itsunblocking position.

4. A' control mechanism for regulating the supply of fluid from a sourceof fluid under pressure to a point of use in response to changes in areference pressure and comprising a casing body providing a pressuresensing chamber at one end .and a valve chamber at its opposite end,said valve chamber constituting a hydraulic cylinder having a ventpassage at one end of said casing body and having a side entrance inletfor connection to said source and a side entrance outlet for connectionto said point of use, a piston like valve body having one end insealingly slidable relation in said cylinder and having its opposite endexposed to fluid entering said inlet, said valve body being mounted insaid cylinder for shifting movement between an unblocking positionwherein said inlet and outlet are in communication and a blockingposition wherein said inlet and outlet are isolated, said valve bodyproviding a passageway for maintaining said inlet in communication withsaid vent passage, a vent cap on said one end of said casing body andspanning said vent passage, a carrier plate movable in said cap andcarrying a vent valve for said vent passage, means for resilientlybiasing said carrier plate to a position in which said vent valve isseated in said vent passage, a pressure responsive bellows in saidpressure sensing chamher and changeable in length in reponse to changesin said reference pressure, and means including compression membersprojecting through said casing body to transmit movement from saidbellows to said carrier plate to position said vent valve in response tochanges in said reference pressure such that when said vent valveunblocks said vent passage fluid flows through said inlet and out saidvent passage but when said vent valve blocks said vent passage fluidpressure acts on the exposed end of said piston-like valve body to forcethe same to its unblocking position.

References Cited in the file of this patent UNITED STATES PATENTS2,274,337 Ritter Feb. 24, 1942 2,275,303 Mantle Mar. 3, 1942 2,345,547Roth et al Mar. 28, 1944 2,366,146 Martin-Hurst Dec. 26, 1944 2,524,444-Ifield Oct. 3, 1950 2,555,004 Rinehart May 29, 1951 2,555,005 WarnekeMay 29, 1951 2,646,814 Mueller July 28, 1953 2,668,415 Lawrence Feb. 9,1954 2,673,025 Labus et a1. Mar. 23, 1954 2,753,882 Bottoms July 10,1956 2,836,345 Gerteis May 27, 1958 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,033,217 May 8, 1962 JosephRaufeisen It is hereby certified that error appeers in the abovenumbered patent requiring co and that the said Letters Patefitt-shouldread as corrected below. Q

Column 5, line zs, for "fludi" after "includi read fl id line, 51

insert means Signed and sealed this 4th day of September 1962.

(SEAL) Y- Attest:

ERNEST w. SWIDER DAVID L LADD Attesting Officer Commissioner of Patents

